This invention relates to split-ring manhole cover supports and more particular to such cover supports that are capable of being gripped more tightly by an existing manhole cover-receiving structure (such as a manhole frame) than are conventional split-ring manhole cover supports.
For simplicity the term "existing manhole cover-receiving structure" is used here to refer to the existing, i.e., fixed in-place frame or other seating receptacle for a removable cover or grating that covers an access hole (i.e., hand hole, tool hole, manhole, catch basin or the like). The term "manhole cover" is used in this application to refer to a removable cover or grating over the access hole. The resulting assembly of a receiving structure and a manhole cover ordinarily is intended to bear vehicular traffic. The term "manhole cover support" or simply "cover support" here means a structure that fits over the existing manhole cover receiving structure, raises its grade, and thereby accommodates a cover or grating at the new elevated grade. The access hole covered usually is a utility enclosure serving, e.g., an electric, gas, water, sewer or storm drainage system.
The preponderance of manholes are circular (in street plan), have circular covers and have existing cover-receiving structures such as frames that have circular access holes, circular sills to support the cover, and circular lateral cover keepers (the latter also sometimes termed "collars"). Accordingly, this specification is directed to generally round manhole cover supports that have ring-like annular elements which are adapted to interact with an existing round manhole cover-receiving structure.
Ordinarily a cover support finds its use when a roadway such as a street or highway is resurfaced with an added layer of paving material or repaved, typically with asphalt concrete or sheet asphalt, to establish a higher grade than immediately before. A principal use for the instant cover support is expected to be in a municipality where axle loads up to 18,182 kg. may have to be resisted by many of these cover supports (as well as serious impact loads from vehicles and snow plows plus a variety of temperature effects, steam leaks, spillage, etc.) without permitting a hazardous dislocation of the cover support or its cover. Often it is desirable also to cushion the cover for resisting wear or reducing noise, and/or to seal the cover and its cover support against a substantial and possibly overloading infiltration of surface water, e.g., storm drainage that otherwise would enter a sanitary sewer system at various manhole locations.
The conventional split ring cover support today has a base ring that is practically uniform in its cross section. Perhaps the least expensive manhole cover support for a circular manhole is a conventional split-ring cover support like the one invented by A. H. R. McCoy. It is disclosed in U.S. Pat. No. 3,891,337 of Jun. 24, 1975, and shows a screw-operated expansion joint, the screw working against the reaction of an abutment projecting from the inside of the base ring. Related ones with various sorts of joint expander means for the split base ring have been developed since then, e.g. the Fier U.S. Pat. Nos. 4,097,171; 4,225,226; and 4,302,126 which show a conventional turnbuckle acting on pivotal eye bolts for the expansion joint and some lever-operated expansion joints, i.e., ones with a spreading link or a pivotally-mounted spreading toggle mechanism.
The force required for physically pulling out vertically a nominally 23-inch steel expansible split ring cover support from a steel manhole frame in which it was very forcefully expanded I found to be 1200 pounds in an actual test. In the test the frame collar was 231/4 inches in diameter at the bottom, 233/4 inches at its top and an inch high; the vertical cross section of the base ring of the cover support was uniformly 3/4-inch thick and one-inch high.
Contrary to expectations the expansion of the base ring of this cover support resulted in tension at the inside periphery of the base ring over quite a large sector of said ring. The ring was expected to be in very high pressure (strong) contact with the frame collar over a fairly large area thereof, the force supplied by the screw means that expanded the base ring spreader being quite high. However, said tension indicated a slight bending of the ring towards its center. Such bending was particularly pronounced and centered opposite to the base ring gap being spread by the screw-operated spreader of the cover support, i.e., opposite to the expansion joint of the split base ring.
The most powerful thrust of the base ring of the tested cover support against the collar of the frame actually occurred in two fairly small sectors, one on each side of spreader; these sectors amounted to roughly no more than about 85.degree.-90.degree. together. The condition of least pressure of the base ring against the collar (the bending inwards) in said about 85.degree.-90.degree. sector was centered in the base ring diametrically opposite to the spreader; this condition was more pronounced in the 60.degree. middle of this sector and even more yet in the 30.degree. middle of such sector. Such sectors which subtend an angle less than 90.degree. are termed "acute sectors" in this application.
An advantage of the present invention over conventional split-ring manhole cover supports includes the ability of the installer to develop a stronger frictional contact (grip) of the collar of the existing cover-supporting structure on the base ring of such inventive cover support than was ever possible before with conventional split ring cover supports. This lessens the likelihood of displacement of the new cover support in service. Additionally, this improved grip can be further enhanced more broadly by the use of a retention component, e.g., a film or deposits or other surfaces comprising polymer having a high coefficient of friction and developing much friction when it is interposed between the film or the deposits are the outer periphery of said base ring and the inside of said collar.
A further advantage of the present invention is the simplicity with which it can be fashioned to hold the manhole cover at a slight tilt to better conform said emplaced cover to the possible increased slope of the new paving from its edge towards its crown after resurfacing or repaving, this while developing a desired selective stiffening in the base ring.